STEP 5: Cutting your paper casting Mold, Backing and Baking

You should have your clay all rolled to a proper thickness, joined if necessary to make it big enough, with your design transferred onto the smoothest side of the clay -- Of course your clay is on waxed paper that is taped securely to a stiff piece of chipboard (like the backing of a good sketchbook). Healable cutting mats are not good because they feel about the same as clay when cutting so you don't feel the depth to cut to very well. And its handy to use the board under it throughout the process, plus you can size it just a little bigger than your clay to make it easier to move around.

You will need an X-acto type knife with a straight blade. A very helpful tool, well worth searching out, is a small "Clay Shaper" flat chisel tip size 0. If you are familiar with "Colour shapers" this is about the same but with a firmer black tip, make sure you get the tiny size 0 one.

hold the knife upright and vertical, with a slight angle for a V or valley cut

We will assume for this first project that you are going to want your letters (or shapes) raised in the casting, which means you will cut them out of the clay for the mold. Rule 2 of casting is "What goes DOWN in the mold goes UP in the casting" which sounds very basic but can really be confusing sometimes. (Rule 1 is "move waxed paper, not clay") Our brains aren't meant to run backwards and casting reverses everything. In fact, take a second to look at that design transferred onto your clay -- if reads forwards, you did it backwards! It should be in reverse (mirror image).

With your clay taped down (waxed paper masking-taped to cardboard), you are ready to start. Hold your knife vertically so you are using the point and have the blade up so only the narrowest part is in the clay - this makes it much easier to turn corners. You will want just a bit of a "V" cut so that the casting will come out of the mold. Think of the tip pointing toward the part of the design that will be removed. If you used acetone transfer it is easy to remember you want to cut away all the black.

cut away the black portions of the polymer clay

It is much easier to avoid "undercutting" (having the angle wrong so there is the opposite of a V) if you cut from the right-hand edge, turning the mold around as needed (unless you're a lefty, then reverse). Do not cut all the right sides and then turn, as the clay will start to heal itself. You can cut small pieces out as you go.

cut out the design with a slight "V" angle so the casting can come out

 If the clay is not cutting cleanly even if you have the knife vertical and move it along smoothly without chopping, you will find it helps immensely to chill the clay. You can simply put a freezer pack underneath the cardboard (helps to have the freezer pack on top of a folded or "scrumpled" towel to stabilize it). You can also put the whole thing in the freezer for a few minutes, but of course you will have to keep putting it back as it warms up.

For this mold, the clay outside the borderline will be cut away.

hold the x-acto fairly vertically and slant with the point towards the clay you are removing

Notice the tip is slanted toward the part being removed.
Cut from the outside of the lines so you are cutting away the line itself, since your slant will make things a bit smaller, and casting tends to make things look smaller and farther apart.

You are hoping to cut through the clay smoothly without cutting through the waxed paper - this can take a little practice so don't stress, but it will make it easier on complicated molds to make sure you get all the waxed paper off, as it will be in one piece.
If you have rough edges or tears at the corners, now is the time the Clay Shaper earns its keep - use it to gently smooth, to press bits back in place, etc. It's great to make it as smooth and neat as you can but after a while you can start to cause as many problems as you fix - most things are fixable later too, when the clay is baked and not likely to get fingernail marks, etc. from over-doing the fixing.

you want the flat chisel tip! size 0, the wooden one is the same tip plus a wire one and may be called a sculpting tool

using the Clay Shaper to hold small bits in place while removing waxed paper

When you are done cutting and smoothing, cover the whole thing with a clean piece of waxed paper, rubbing lightly to help it adhere (especially if you have small loose pieces of clay in your design). Cut away or loosen the tape, then place another cardboard on top and carefully flip it over. Remove the original cardboard and carefully peel every bit of waxed paper off your clay.
Now you can see your design "forwards" and see how you like it - don't worry too much if it seems off, this side will be against the background and little variations really won't show. If you really think you cut it wrong you can add waxed paper again and flip it back and recut.
 If you have unconnected pieces like the counters in letters, they will be extra secure if you can put just a tiny bit of Sculpey Diluent or Softener (I think its the same stuff, they've changed the name) - barely a drop on an old brush will do several spots.

Diluent or Softener - this bottle has lasted 11 years, it doesn't take much

there's enough in this drop for many spots to be wet enough so they will adhere better in the mold

 Adding the backing (OR second layer in a multiple layer piece)
 Your backing layer should be thicker - if you are using a pasta machine use the thickest setting - and it needs to be at least 3/4" bigger all around than the border of the first piece.

thicker backing layer ready to lay over flipped-over cut-out design - note everything was cut away outside of border

laying it down as centered as you can

After double-checking that there is no waxed paper anywhere on top of your design, you will take the thicker clay (on its waxed paper, of course) and carefully lay it over the design, (wax paper up-clay onto clay) keeping it as centered as you can. It helps if you can start from one side and press it on lightly to help keep from getting bubbles between the layers.

carefully adding a second  layer of polymer clay over the "forwards" design

 Rub lightly, especially if there are small pieces you want to make sure are sticking to the backing layer. Now slip cardboard under and carefully flip it back over, then remove the wax paper that is over the design.

slip cardboard under and flip it back over

remove waxed paper off top of design

The backing layer covers up the "forwards" design - so if you have a backing layer on and your design is not reversed, oops, you didn't flip it! if you are quick and it hasn't adhered you can probably carefully pull it off and do it right.You can use the clay shaper again to smooth and fix, especially small pieces that might need to be put back into position.

on this mold, the yellow is a second layer and another backing will be added after more cutting.

Trim it evenly, leaving plenty of space for your deckle to be made. If it follows the border line of the first piece it will be easier to tell where to make the edge of the casting. If you think you see air bubbles, stick with a pin and smooth over gently with finger. If the hole isn't wanting to disappear you can fill it or smooth it after baking - that's better than making dents from trying too hard.

Bake! a smooth ceramic tile(under $1 at Lowe's) is great for baking molds on, but not required - a cookie sheet, even the cardboard will work. Leave the waxed paper under it for now.
Premo bakes at 275 for 30 minutes for 1/4 inch thickness. You can hold a ruler to the edge to gauge thickness if you want. The small molds like the bird shown above or "joy" below need about 20-25 minutes. If your oven isn't overheated, longer will not hurt. If it comes out with bubbles, or warps, you can lay a tile on top (smooth side down of course)  to hold it flat while it cools and it will stay that way.

A finished mold. It would be much easier to cast with a nice, even edge if the backing layer had been cut wider and more evenly matched to the shape

Its best to use a dedicated oven, like a good quality toaster oven, since the fumes are definitely not healthy - at least use all the ventilation you can. Afterwords you can reheat the oven to a higher temp and then open and ventilate some more to make sure fumes are out and won't be in your food (I hope - if I die of polymer clay some day, will we even know?). Toaster ovens' thermostats can be pretty unreliable so you might invest in an oven thermometer.
That's it! it takes longer to describe than to make, really pretty simple. Just cut out the design being careful not to undercut, flip over to add a backing layer, trim and bake.

"Making the Casting" tutorial will be posted very soon.


Remember, for personal, live instruction and experienced problem-prevention, you can gather a group for a workshop